Turbochargers are conventionally used in internal combustion engines to increase the amount of injected intake air so as to increase the output of the engine. In general, the turbocharger consists of a turbine wheel mounted in the exhaust manifold of the engine and a compressor coupled to the turbine wheel and mounted in the intake manifold of the engine. As exhaust gases flow past the turbine wheel it is rotated, causing the compressor to also rotate which increases the pressure of the intake air being charged into the engine cylinders, mixing with fuel and thereafter undergoing combustion.
A known objective with turbocharger design is the attainment of efficient operation over the entire range of operating speeds of the engine. For example, if a turbocharger is designed to provide maximum torque at low engine speeds, at high engine speeds the turbine wheel will rotate at an excessive speed, eventually causing damage by supplying too much air to the engine, and causing excessive wear of the turbocharger parts. On the other hand, if a turbocharger is provided to operate most efficiently at high engine speeds, the efficiency of the turbocharger will be undesirably low when the engine is running at low speeds.
Variable geometry components in the turbocharger compressor, the turbocharger turbine, or both, commonly include variable nozzle vanes ahead of the turbine wheel and/or variable diffuser vanes in the compressor component. Variable nozzle vanes ahead of the turbine wheel are connected together so that the throat area of each nozzle passage can be reduced over the low engine speed range and increased as the engine speed approaches its maximum, so that the turbocharger speed is kept within a safe operating range.
An internal combustion engine may operate in a variety of different closed loop and open loop modes based upon a variety of monitored engine operating parameters. Some typical operating closed loop modes include a cold mode, a warm mode, a cranking mode, a low idle mode, and a high idle mode. In-between the low idle mode and the high idle mode, the engine runs in an open loop mode where fuel is delivered based on engine throttle position and engine speed. Various engine operating parameters may be monitored to determine the engine operating mode including engine speed, throttle position, vehicle speed, coolant temperature, and oil temperature, as well as others. In each operating mode it is not uncommon to use different techniques to determine the amount of fuel to deliver to the engine during a fuel delivery cycle. For example, different fuel rate maps might be utilized in two different modes or a fuel rate map might be used in one mode, and in another mode an engine speed governor with closed loop control may be used. An electronic control module that regulates the quantity of fuel that the fuel injector dispenses includes software in the form of maps or multi-dimensional lookup tables that are used to define optimum fuel system operational parameters. One of these maps may be a torque map which uses the actual engine speed signal to produce the maximum allowable fuel quantity signal based on the horsepower and torque characteristics of the engine. Another map may be the emissions, or smoke limiter map, which limits the amount of smoke produced by the engine as a function of air manifold pressure or boost pressure, ambient temperature and pressure, and engine speed. The maximum allowable fuel quantity signal produced by the smoke map limits the quantity of fuel based on the quantity of air available to prevent excess smoke.
Various control systems for VGTs are known in the art. U.S. Pat. No. 5,123,246 pertains to a control system that takes into account engine operating parameters, but does not disclose means for controlling the engine during different operating modes. U.S. Pat. No. 4,671,068 teaches a control system for a VGT that switches between open loop and closed loop modes, using atmospheric pressure and boost pressure. It is often desirable, however, to use different engine operating parameters to determine when to switch between open loop and closed loop modes.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.